Integrated waste heat recovery

ABSTRACT

A system and method of operating a waste heat recovery system for a vehicle is provided. The system includes an expander/compressor portion mechanically linked to wheels of the vehicle, the expander/compressor portion including an inlet valve and an exhaust valve. A combustion engine is provided having an exhaust portion. A working fluid path is thermally coupled between the combustion engine and a working fluid, the working fluid path being fluidly coupled to the expander/compressor portion. A boiler portion is fluidly coupled to the working fluid path, the boiler portion further being thermally coupled to the exhaust portion. An accumulator tank portion having a cavity is operative to receive and store the working fluid, the accumulator tank portion fluidly coupled to the inlet valve and the exhaust valve. A condenser is fluidly coupled to the working fluid path and the exhaust valve.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Patent Application Ser. No. 61/746,704 filed Dec. 28, 2012 which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The subject invention relates to combustion engines and waste heat recovery in combustion engines.

BACKGROUND

Combustion engines such as internal combustion engines used in vehicles consume fuel through a combustion process. The combustion process produces heat that is wasted when the heat is not used for productive purposes.

Accordingly, it is desirable to provide a system that utilizes the waste heat to provide more efficient operation of the system.

SUMMARY OF THE INVENTION

According to one embodiment, a system and method of operating a waste heat recovery system for a vehicle is provided. The system includes an expander/compressor portion mechanically linked to wheels of the vehicle, the expander/compressor portion including an inlet valve and an exhaust valve. A combustion engine is provided having an exhaust portion. A working fluid path is thermally coupled between the combustion engine and a working fluid, the working fluid path being fluidly coupled to the expander/compressor portion. A boiler portion is fluidly coupled to the working fluid path, the boiler portion further being thermally coupled to the exhaust portion. An accumulator tank portion having a cavity is operative to receive and store the working fluid, the accumulator tank portion fluidly coupled to the inlet valve and the exhaust valve. A condenser is fluidly coupled to the working fluid path and the exhaust valve

According to another embodiment, a waste heat recovery system for a vehicle is provided. The system including an expander/compressor portion mechanically linked to wheels of the vehicle, the expander/compressor portion including a primary inlet valve, a secondary inlet valve and an exhaust valve. A combustion engine is provided having an exhaust portion, the exhaust portion having an exhaust gas path. A working fluid path is provided having a working fluid, the working fluid path being thermally coupled to the combustion engine and fluidly coupled to the to the secondary inlet valve of the expander/compressor portion. A boiler portion is provided having a heat exchange portion thermally coupled to the exhaust gas path. An accumulator tank portion that includes a cavity is operative to receive and store the working fluid, the accumulator tank portion fluidly coupled to the working fluid path and the primary inlet valve. A condenser portion is fluidly coupled between the exhaust valve and the boiler portion.

According to yet another embodiment a method of operating a waste heat recovery system for a vehicle having wheels is provided. The method including operating a combustion engine to exchange heat with a working fluid. The working fluid is output from the combustion engine to an accumulator tank. The working fluid is stored in the accumulator tank.

The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which:

FIG. 1 illustrates an exemplary heat waste recovery system;

FIG. 2 illustrates an exemplary “driving vehicle mode” of the system of FIG. 1;

FIG. 3 illustrates an exemplary “accumulator charging mode” of the system of FIG. 1;

FIG. 4 illustrates an exemplary “accumulator tank depletion mode” of the system of FIG. 1;

FIG. 5 illustrates an exemplary “regenerative breaking mode” of the system;

FIG. 6 illustrates a graphical representation of the torque output by the system over time of FIG. 1;

FIG. 7 illustrates an another embodiment of a waste heat recovery system;

FIG. 8 illustrates an exemplary “driving vehicle mode” of the system of FIG. 7;

FIG. 9 illustrates an exemplary “accumulator charging mode” of the system of FIG. 7;

FIG. 10 illustrates an exemplary “accumulator tank depletion mode” of the system of FIG. 7;

FIG. 11 illustrates an exemplary “regenerative breaking mode” of the system of FIG. 7; and

FIG. 12 illustrates an exemplary embodiment of a control system for a waste heat recovery system.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Combustion engines, such as internal combustion engines for example, produce of waste heat during the combustion process. The waste heat was typically transferred into the atmosphere, resulting in a significant inefficiency in the engine system. The inefficiency increases the fuel needed to drive the system, and reduces the fuel economy of the system. The methods and systems described below provide a more efficient engine system for a vehicle using the waste heat produced by the engine and from braking or slowing of the vehicle to produce steam that is used to assist in driving the vehicle.

In accordance with an exemplary embodiment of the invention, FIG. 1 illustrates an exemplary system 100. The system 100 includes a combustion engine 102 that receives intake air via a turbo charger 104 and outputs exhaust gasses via a catalyst portion 106. The engine 102 is cooled by a high pressure (HP), low temperature (LT) working fluid, such as a refrigerant such as R134a for example. The working fluid receives engine heat from for example, coolant water that circulates through a heat exchanger portion 103. A pump 105 may circulate the coolant water through the engine 102 and the heat exchanger portion 103. The HP/LT fluid received by the engine 102, and following a heat exchange in the engine, is output as HP medium temperature (MT) fluid to a boiler portion 108. The boiler portion 108 is a heat exchanging device that may include, for example, tubes that propagate the working fluid and receive thermal energy from the exhaust gasses (output by the engine 102) that flow through the boiler portion 108 (around the tubes propagating the working fluid) and transfer heat to the working fluid. The boiler portion 108 outputs the working fluid as a high pressure and high temperature (HT) gas. An exhaust flow regulating valve 107 may be used to regulate the temperature of the boiler portion 108, and in-turn, the pressure of the working fluid output by the boiler portion 108. The exhaust flow regulating valve 107 is operative to control the flow of the exhaust gas from the engine 102 and regulate the amount of exhaust that passes through the boiler portion 108 or is output to the atmosphere via a boiler bypass path 109. A boiler check valve 110 is arranged to control the flow of working fluid from the boiler portion 108 to limit or check the backflow of working fluid into the boiler portion 108. A boiler recirculation valve 111 is arranged to control the flow of working fluid that may recirculate to the heat exchanger portion 103. For a working fluid that includes R134a refrigerant the temperature and pressure ranges may include for example: HT, 125° C.-200° C.; MT, 55° C.-125° C.; LT<55° C. HP, 40 Bar-150 Bar; MP, 15 Bar-40 Bar; LP 5 Bar-15 Bar.

An accumulator tank portion 112 is arranged with a first accumulator control valve 114 that controls the flow of working fluid from the boiler portion 108 into the accumulator tank portion 112. An expander/compressor (E/C) portion 116 is arranged with inlet valves 118 and exhaust valves 120 that control the flow of working fluid into and out of the E/C portion 116. The E/C portion 116 may be mechanically linked to wheels 101 of the vehicle. A second accumulator control valve 122 is arranged to control the flow of the working fluid that may be output by the expander/compressor portion 116 to the accumulator tank portion 112. A condenser portion 124 is operative to receive low pressure (LP) high temperature working fluid output by the expander/compressor portion 116, and condense the working fluid from a gas to a liquid. A condenser control valve 126 is arranged to control the flow of the working fluid into the condenser portion 124. A condenser check valve 113 may be arranged to limit or check a backflow of the working fluid into the condenser portion 124. A pump portion 128 may be mechanically driven by the engine 102 or may be electrically driven via an electrical power source such as, for example, a battery (not shown). The pump portion 128 is arranged to receive LP-LT working fluid from the condenser and output HP-LT working to the engine 102. A pressure regulating portion 130 is arranged to regulate the pressure of the working fluid output by the pump portion 128.

The system 100 described above is operative to use the working fluid to drive the vehicle during a variety of operational modes of the vehicle. In this regard, the operation of the system 100 in a number of operating modes is described below. As described herein, “drive” includes imparting a force operative to move or affect the movement of a component or object.

The system 100 may operate in a “warm up mode” that is operative to heat the engine quickly during a warm up period following starting the engine 102. In this regard, referring to FIG. 1, once the engine 102 is started, the working fluid flows through the boiler portion 108 and is heated by the exhaust gas output by the engine 102. The boiler recirculation valve 111 is open, which provides a recirculation path for the working fluid that is output by the boiler portion 108 to flow into the heat exchanger portion 103 to heat the coolant water in the engine 102. The pump 128 is operative to pressurize and circulate the working fluid. The “warm up mode” decreases warm up time of the engine 102. Once the engine 102 has reached a desired operating temperature, the system 100 may transition into another operating mode.

FIG. 2 illustrates an exemplary “driving vehicle mode” of the system 100. In the vehicle driving mode, the engine 102 may be operating by combusting fuel, and providing mechanical torque to the drive train of the vehicle alternatively, the engine 102 may be idle, or the engine 102 may not be combusting fuel (i.e. if the engine 102 is not combusting fuel, the engine 102 may provide thermal energy to the working fluid due to residual heat that is stored in the engine components and the catalyst portion 106 following the operation of the engine 102). Referring to FIG. 2, the working fluid enters the heat exchanger portion 103 as a HP-LT liquid, and exchanges heat with the engine 102. The working fluid exits the heat exchanger portion 103 as a HP-MT fluid and enters the boiler portion 108. The working fluid exchanges heat with exhaust gas from the engine 102 (via the catalyst 106) in the boiler portion 108, which outputs the working fluid as a HP-HT gas. The first accumulator control valve 114 and the second accumulator control valve 122 are closed. The inlet valves 118 and the exhaust valves 120 of the E/C portion 116 are intermittently opened and aligned such that the working fluid in a HP-HT state enters the expander/compressor portion 116 and expand to drive the E/C portion 116. The driving of the E/C portion 116 by the working fluid is operative to drive the wheels 101 of the vehicle. The condenser control valve 126 is open such that the E/C portion 116 outputs the working fluid as a LP-HT or as LP-MT gas to the condenser portion 124. The condenser portion 124 condenses the working fluid to a LP-LT liquid and outputs the working fluid to the pump portion 128. The boiler recirculation valve 111 is closed. The pump portion 128 pressurizes the working fluid into a HP-LT liquid that is provided to the engine 102.

FIG. 3 illustrates an exemplary “accumulator charging mode” of the system 100. In the accumulator charging mode, the system 100 is operative to provide HP-HT working fluid gas to the accumulator tank portion 112. In this regard, referring to FIG. 3, the boiler recirculation valve 111 is closed. The HP-HT working fluid is output from the boiler portion 108. The first accumulator control valve 114 is in an open state and the second accumulator control valve 122 is in a closed state such that the accumulator tank receives and stores the HP-HT working fluid output from the boiler portion 108. The condenser control valve 126 is either in a closed or open state. The inlet valves 118 and the exhaust valves 120 of the E/C portion 116 are inactive in that they remain closed to prevent HP-HT gas from entering or exiting the E/C.

FIG. 4 illustrates an exemplary “accumulator tank depletion mode” of the system 100. In the accumulator tank depletion mode, the system is operative to provide HP-HT working fluid to the E/C portion 116. The boiler recirculation valve 111 is closed. The E/C portion 116 is aligned to receive the HP-HT working fluid and expand the working fluid to drive the wheels 101 of the vehicle. In this regard, referring to FIG. 4, the first accumulator control valve 114 is in an open state. The second accumulator control valve 122 is in a closed state. The accumulator portion 112 outputs HT-HP working fluid to the E/C portion 116. In this state, the accumulator 112 pressure exceeds the pressure at the outlet of the boiler 108, thereby closing the one-way valve 110 which in turns prevents back-flow into the boiler from the accumulator. The states of the inlet valves 118 and the exhaust valves 120 of the E/C portion 116 are controlled to allow the E/C portion 116 to receive and expand the HT-HP working fluid from the accumulator tank portion 112 and drive the E/C portion 116, which drives the wheels 101 of the vehicle. The condenser control valve 126 is in an open state to receive the LP-HT working fluid output by the E/C portion 116 and condense the working fluid as described above.

FIG. 5 illustrates an exemplary “regenerative breaking mode” of the system 100. In the regenerative breaking mode, the engine 102 may be idle or not combusting fuel. The E/C portion 116 is aligned to receive the working fluid as a LP-MT gas from the boiler portion 108 and compress the working fluid into a HP-HT gas. The HT-HP working fluid is output from the E/C portion 116 to the accumulator tank portion 112. In this regard, referring to FIG. 5, the exhaust flow regulating valve 107 may be aligned to regulate the engine exhaust gas to bypass the boiler portion 108. The boiler recirculation valve 111 is closed. The first accumulator control valve 114 is in a closed state. The inlet valves 118 and the exhaust valves 120 are aligned in an open state such that the MP-MT fluid output by the boiler portion 108 is compressed by the E/C portion 116 into a HP-HT fluid. The wheels 101 of the vehicle drive the E/C portion 116, which in turn compresses the working fluid. The condenser control valve 126 is in a closed state. The second accumulator control valve 122 is in an open state such that the HP-HT working fluid is received and stored in the accumulator tank portion 112.

FIG. 6 illustrates a graphical representation of the torque output by the system 100 over time. In this regard, the “desired torque” “a” curve illustrates a desired torque response of the system 100. The “internal combustion engine (ICE) torque” “b” curve illustrates the torque output by the engine 102. The “heat recovery torque” “c” curve illustrates the torque output by the E/C portion 116 using working fluid received from the boiler portion 108. The “heat recovery+ICE torque” “d” curve illustrates the torque output by the E/C portion 116 and the engine 102.

In this regard, the region I illustrates the system 100 in a constant torque output state in region I the system 100 may operate in the “driving vehicle mode” described above. The region II illustrates the system 100 in an increasing torque output state during the operation of the system 100 in region II the system 100 may also operate in the “driving vehicle mode” described above. The desired torque curve is greater than the heat recovery+ICE torque curve in the region III. When the desired torque curve is greater than the heat recovery+ICE torque curve, the system 100 may operate in the “accumulator tank depletion mode” such that working fluid stored in the accumulator tank portion 112 is provided to the E/C portion 116 to provide additional working fluid to drive the E/C portion 116 such that the E/C portion 116 outputs additional torque to raise the output torque to approximately match the desired torque curve.

In the region IV, the system 100 is outputting a substantially constant torque. In the region IV, the system 100 may also operate in the “driving vehicle mode” described above. In the region V, the system 100 is outputting a reduced torque. The region V heat recovery+ICE torque curve is greater than the desired torque curve. During the region V, the system 100 may operate in a “regenerative breaking mode” or a “accumulator charging mode” as described above to provide HP-HT working fluid to the accumulator tank portion 112. The system 100 in the region VI is outputting a substantially constant torque, and may operate in the “driving vehicle mode” as described above.

FIG. 7 illustrates another embodiment of a system 700 that includes a two stage E/C portion 716. The system 700 is similar in operation as the system 100 described above. The system 700 includes a first pressure regulating portion 730 and a second pressure regulating portion 732. The first pressure regulating portion 730 is operative to receive working fluid from the pump 128 and regulate the pressure of the output working fluid that is output to the boiler portion 108. The second pressure regulating portion 732 is operative to receive working fluid output by the first pressure regulating portion 730 and regulate the pressure of the working fluid output to the engine heat exchanger portion 103.

FIG. 8 illustrates an exemplary “driving vehicle mode” of the system 700. A portion of the working fluid exits the first pressure regulating portion 730 as a HP-LT fluid and enters the boiler portion 108. The working fluid exchanges heat with the exhaust gasses from the engine 102 and is output from the boiler portion 108. The primary expander control valve 702 is in an open state. The working fluid enters the E/C portion 716 via the primary inlet valves 718. Another portion of the working fluid is output from the pump 128 to the engine coolant heat exchanger 103 where the working fluid exchanges heat with the engine 102 and is output by the engine as a HP-MT fluid. The working fluid passes through the secondary expander control valve 706 and enters the E/C portion 716 via the secondary inlet valves 704. The working fluid in the E/C portion 716 expands and drives the E/C portion that is mechanically linked to the wheels 101 of the vehicle. The working fluid exits the E/C portion via the exhaust valves 120 and enters the condenser 124 where the working fluid is condensed into a LP-LT fluid that is input to the pump portion 128.

FIG. 9 illustrates an exemplary “accumulator charging mode” of the system 700. In the accumulator charging mode, the system 700 is operative to provide HP-HT working fluid gas output from the boiler portion 108 to the accumulator tank portion 112. The accumulator control valve 114 is in an open state and the primary expander control valve 702 is in a closed state such that the accumulator tank receives and stores the HP-HT working fluid output from the boiler portion 108.

FIG. 10 illustrates an exemplary “accumulator tank depletion mode” of the system 700. In the accumulator tank depletion mode, the system is operative to provide HP-HT working fluid to the E/C portion 716. The E/C portion 716 is aligned to receive the HP-HT working fluid and expand the working fluid to drive the wheels 101 of the vehicle. In this regard accumulator control valve 114 is in an open state and the primary expander control valve 702 is in an open state. The secondary expander control valve 706 is in a closed state. The accumulator portion 112 outputs HT-HP working fluid to the E/C portion 716. The states of the inlet valves 718 and the exhaust valves 120 of the E/C portion 716 allow the E/C portion 716 to receive and expand the HT-HP working fluid from the accumulator tank portion 112 and drive the E/C portion 716, which drives the wheels 101 of the vehicle.

FIG. 11 illustrates an exemplary “regenerative breaking mode” of the system 700. In the regenerative breaking mode, the engine 102 may be idle or may not be combusting fuel. The E/C portion 716 is aligned to receive the working fluid as a LP-MT gas from the engine 102 and compress the working fluid into a HP-HT gas by being driven by the wheels 101 of the vehicle. The HT-HP working fluid is output from the E/C portion 716 to the accumulator tank portion 112. In this regard the secondary expander control valve 706 is in an open state. The secondary inlet valves 704 are in an open state such that LP-MT working fluid is input into the E/C portion 716. The exhaust valves 120 are in a closed state, and the primary inlet valves 718 are in an open state such that the HT-HP working fluid is output by the E/C portion 716 via the primary inlet valves 718. The primary expander control valve 702 and the accumulator control valves 114 are in an open state such that the HP-HT working fluid is received and stored in the accumulator tank portion 112.

FIG. 12 illustrates an exemplary embodiment of a control system 1200 that includes a processor 1202 that is operative to control the systems described above using logic. The processor 1202 that is communicatively connected to input devices 1206, such as sensors and other diagnostic devices operative to sense states of the systems 100 and 700 (of FIGS. 1 and 7) for example. The processor 1202 is communicatively connected to a memory device 1208. The processor 1202 is operative to process signals input from the input devices 1206 and perform control logic to output control signals 1210 that are operative to control, for example, the engine 102, valves, and other components of the systems 100 and 700 described above. The control system 1200 may include a display device 1204 communicatively connected to the processor 1202. Though the illustrated embodiment includes a single processor 1202, the processor 1202 may include any number of processors or subsystems that are operative to control the systems 100 and 700.

The methods and systems described herein provide a system for a vehicle that recovers waste heat from an engine and from braking or slowing the vehicle and utilizes the waste heat to drive the wheels of the vehicle or other associated subsystems of the vehicle. The use of the waste heat provides improved efficiency in the systems.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application. 

What is claimed is:
 1. A waste heat recovery system for a vehicle, the system comprising: an expander/compressor portion is mechanically linked to wheels of the vehicle, the expander/compressor portion including an inlet valve and an exhaust valve; a combustion engine having an exhaust portion; a working fluid path having a working fluid, the working fluid path being thermally coupled to exchange heat between the combustion engine and the working fluid, the working fluid path being fluidly coupled to the expander/compressor portion; a boiler portion having a heat exchange portion that is fluidly coupled to the working fluid path, the boiler portion further being thermally coupled to the exhaust portion; an accumulator tank portion having a cavity that is fluidly coupled to receive and store the working fluid, the accumulator tank portion being fluidly coupled to the working fluid path, the inlet valve and the exhaust valve of the expander/compressor portion; and a condenser fluidly coupled to the working fluid path and the exhaust valve.
 2. The system of claim 1, further comprising a pump portion fluidly coupled to the working fluid path between the condenser and the combustion engine.
 3. The system of claim 1, further comprising a processor operative to control the system, wherein the processor is operative to control a vehicle driving mode that includes: operating the combustion engine to exchange heat with the working fluid; control an output of the working fluid from the boiler portion to the expander/compressor portion; and control the expander/compressor portion such that the expander/compressor portion drives the wheels of the vehicle.
 4. The system of claim 1, further comprising a processor operative to control the system, wherein the processor is operative to control an accumulator charging mode that includes: operating the combustion engine and exchanging heat with the working fluid; controlling an output of the working fluid from the boiler portion to the accumulator tank portion; and controlling the accumulator tank portion to receive and store the working fluid.
 5. The system of claim 1, further comprising a processor operative to control the system, wherein the processor is operative to control an accumulator tank depletion mode that includes: controlling the accumulator tank portion to output the working fluid to the expander/compressor portion; and controlling the expander/compressor portion to receive the working fluid from the accumulator tank portion and drive the wheels of the vehicle.
 6. The system of claim 1, further comprising a processor operative to control the system, wherein the processor is operative to control a regenerative breaking mode that includes: controlling the expander/compressor portion to receive the working fluid from the boiler portion, compressing the working fluid by being driven by the wheels of the vehicle, and outputting compressed working fluid to the accumulator tank portion; and controlling the accumulator tank portion to receive and store the compressed working fluid.
 7. The system of claim 1, further comprising a processor operative to control the system, wherein the processor is operative to control a warm up mode that includes controlling an output of the working fluid from the boiler portion to the engine such that the working fluid heats the engine.
 8. The system of claim 1, wherein the boiler portion is operative to receive the working fluid from the combustion engine at a high pressure and medium temperature and output the working fluid at a high pressure and high temperature.
 9. A waste heat recovery system for a vehicle, the system comprising: an expander/compressor portion mechanically linked to wheels of the vehicle, the expander/compressor portion including a primary inlet valve, a secondary inlet valve and an exhaust valve; a combustion engine having an exhaust portion, the exhaust portion having an exhaust gas path; a working fluid path having a working fluid, the working fluid path being thermally coupled to the combustion engine and fluidly coupled to the to the secondary inlet valve of the expander/compressor portion; a boiler portion having a heat exchange portion thermally coupled to the exhaust gas path; an accumulator tank portion that includes a cavity operative to receive and store the working fluid, the accumulator tank portion fluidly coupled to the working fluid path and the primary inlet valve; and a condenser portion fluidly coupled between the exhaust valve and the boiler portion.
 10. The system of claim 9, further comprising a pump portion fluidly coupled to the working fluid path between the condenser portion and the combustion engine.
 11. The system of claim 9, further comprising a processor operative to control the system, wherein the processor is operative to control a vehicle driving mode that includes: operating the combustion engine to exchange heat with the working fluid; controlling an output of the working fluid from the combustion engine to the expander/compressor portion; controlling an output of the working fluid from the boiler portion to the expander/compressor portion; and controlling the expander/compressor portion such that the expander/compressor portion drives the wheels of the vehicle.
 12. The system of claim 9, further comprising a processor operative to control the system, wherein the processor is operative to control an accumulator charging mode that includes: operating the combustion engine to exchange heat with the working fluid; controlling an output of the working fluid from the boiler portion to the accumulator tank portion; and controlling the accumulator tank portion to receive and store the working fluid.
 13. The system of claim 9, further comprising a processor operative to control the system, wherein the processor is operative to control an accumulator tank depletion mode that includes: controlling the accumulator tank portion to output the working fluid to the expander/compressor portion; and controlling the expander/compressor portion to receive the working fluid from the accumulator tank portion and drive the wheels of the vehicle.
 14. The system of claim 9, further comprising a processor operative to control the system, wherein the processor is operative to control a regenerative breaking mode that includes: controlling the expander/compressor portion to receive the working fluid from the boiler portion, compressing the working fluid by being driven by the wheels of the vehicle, and outputting compressed working fluid to the accumulator tank portion; and controlling the accumulator tank portion to receive and store the compressed working fluid.
 15. The system of claim 9, further comprising a processor operative to control the system, wherein the processor is operative to control a warm up mode that includes controlling an output of the working fluid from the boiler portion to the engine such that the working fluid heats the engine.
 16. The system of claim 9, wherein the boiler portion is operative to receive the working fluid from the combustion engine at a high pressure and medium temperature and output the working fluid at a high pressure and high temperature.
 17. A method of operating a waste heat recovery system for a vehicle having wheels, the method comprising: operating a combustion engine to exchange heat with a working fluid; outputting the working fluid from the combustion engine to an accumulator tank; and storing the working fluid in the accumulator tank.
 18. The method of claim 17 further comprising: following the storing the working fluid in the accumulator tank, outputting the working fluid from the accumulator tank to an expander/compressor portion; driving the expander/compressor portion with the working fluid; and driving the wheels of the vehicle with the expander/compressor portion.
 19. The method of claim 18, further comprising: following the driving the wheels of the vehicle with the expander/compressor portion, receiving the working fluid in the expander/compressor portion; driving the expander/compressor portion with the wheels of the vehicle; compressing the working fluid with the expander/compressor portion; outputting compressed working fluid from the expander/compressor portion to the accumulator tank portion; and storing the compressed working fluid in the accumulator tank portion.
 20. The method of claim 17, further comprising: outputting the working fluid from the accumulator tank portion to an expander/compressor portion; driving the expander/compressor portion with the working fluid; and driving the wheels of the vehicle with the expander/compressor portion. 